When drive current is supplied to drive a motor, the coil in the motor generates heat. Therefore, hitherto, various techniques to dissipate heat generated by the coil of a motor to the outside have been proposed. For example, a technique of providing a passage through which cooling water flows in the housing of a motor to dissipate heat generated by the coil to the outside via the cooling water is known.
A motor having a cooling water passage according to the related art is described in, for example, JP-A-8-322170. The motor in JP-A-H08-322170 has a cooling passage in the yoke positioned in the periphery of a stator core (Paragraph 0008, FIG. 1).
In the motor in JP-A-H08-322170, heat generated by a stator winding is conducted to the outside in a radial direction and is transferred to the yoke (Paragraph 0010). In addition, the heat is absorbed by cooling water in the cooling passage provided in the yoke.
However, in the motor in JP-A-H08-322170, the cooling passage is not provided at a position on the outside in the radial direction of the stator winding (FIG. 1). Therefore, the heat generated by the stator winding is conducted to the outside in the radial direction, is further transferred to the inside of the yoke in an axial direction, and reaches the cooling flow path. In this structure, when the amount of heat generated by the stator winding is increased, there is concern that the heat may not be sufficiently conducted from the stator winding to the cooling passage.